In the manufacture of paper products, it is often desirable to enhance physical and/or optical properties by the addition of chemical additives. Typically, chemical additives such as softeners, colorants, brighteners, strength agents, etc. are added to the fiber slurry upstream of the headbox in a paper making machine during manufacturing to impart certain attributes to the finished product. These chemical additives are usually mixed in a stock chest or stock line where the fiber slurry has a fiber consistency of from between about 0.15 to about 5 percent or spraying the wet or dry paper or tissue during production.
One disadvantage of adding a chemical additive at each paper machine is that the manufacturer has to install equipment on each paper machine to accomplish the chemical additive addition. This, in many cases, is a costly proposition. In addition, the uniformity of the finished product coming off of each paper machine may vary depending upon how the chemical additive was added, variations in chemical additive uniformity and concentrations, the exact point of chemical additive introduction, water chemistry differences among the paper machines as well as personnel and operational differences of each paper machine.
Another difficulty associated with wet end chemical additive addition is that the water soluble or water dispersible chemical additives are suspended in water and are not completely adsorbed or retained onto the fibers prior to formation of the wet mat. To improve adsorption of wet end chemical additives, the chemical additives are often modified with functional groups to impart an electrical charge when in water. The electrokinetic attraction between charged chemical additives and the anionically charged fiber surfaces aids in the deposition and retention of chemical additives onto the fibers. Nevertheless, the amount of the chemical additive that can be adsorbed or retained in the paper machine wet end generally follows an adsorption curve exhibiting diminishing incremental adsorption with increasing concentration, similar to that described by Langmuir. As a result, the adsorption of water soluble or water dispersible chemical additives may be significantly less than 100 percent, particularly when trying to achieve high chemical additive loading levels. The use of water insoluble chemical additives in the water systems of papermaking processes is even more problematic and typically provides even poorer loading levels. Water insoluble chemical additives or water nondispersible chemical additives cannot typically be used in such water systems unless in the form of an emulsion.
Consequently, at any chemical addition level, and particularly at high addition levels, a fraction of the chemical additive is retained on the fiber surface. The remaining fraction of the chemical additive remains dissolved or dispersed in the suspending water phase. These unadsorbed or unretained chemical additives can cause a number of problems in the papermaking process. The exact nature of the chemical additive will determine the specific problems that may arise, but a partial list of problems that may result from unadsorbed or unretained chemical additives includes: foam, deposits, contamination of other fiber streams, poor fiber retention on the machine, compromised chemical layer purity in multi-layer products, dissolved solids build-up in the water system, interactions with other process chemicals, felt or fabric plugging, excessive adhesion or release on dryer surfaces, physical property variability in the finished product.
Therefore, what is lacking and needed in the art is an improved method for using water insoluble chemical additives, providing more consistent water insoluble chemical additive additions to the pulp fiber and a reduction or elimination of unretained water insoluble chemical additives in the process water on a paper machine. The method minimizes the associated manufacturing and finished product quality problems that would otherwise occur with conventional wet end chemical addition at the paper machine.
It has now been discovered that water insoluble chemical additives can be applied to pulp fibers at high and/or consistent levels with reduced amounts of unretained water insoluble chemical additives present in the papermaking process water after the treated pulp fiber has been redispersed in water. This is accomplished by treating a fibrous web prior to the finishing operation at a pulp mill with a water insoluble chemical additive, completing the finishing operation, redispersing the finished pulp at the paper mill and using the finished pulp in the production of a paper product.
Hence in one aspect, the invention resides in a method for preparing chemically treated pulp fibers. The method comprises creating a fiber slurry comprising process water and virgin pulp fibers. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and formed into a wet fibrous web. The wet fibrous web is dried to a predetermined consistency thereby forming a dried fibrous web. The dried fibrous web is treated with a water insoluble chemical additive thereby forming a chemically treated dried fibrous web containing chemically treated pulp fibers wherein the chemically treated pulp fibers have an increased or improved level of chemical retention of the water insoluble chemical additive and have a level of chemical retention of the water insoluble chemical additive is between about 25 to about 100 percent retention of the applied amount of the water insoluble chemical additive when the chemically treated pulp fibers are redispersed in water. The level of chemical retention of the water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the water insoluble chemical additive. The improved level of chemical retention of the water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the water insoluble chemical additive. It is understood that the value for the lower limit is less than the value for the upper limit. The chemically treated pulp fiber may be then used in a separate process to produce paper products.
In another aspect, the invention resides in a method for applying a water insoluble chemical additive to pulp fiber. The method comprises mixing pulp fibers with process water to form a fiber slurry. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and forming a wet fibrous web. The wet fibrous web is dewatered to a predetermined consistency thereby forming a dewatered fibrous web. A water insoluble chemical additive is applied to the dewatered fibrous web, thereby forming a chemically treated dewatered fibrous web containing chemically treated pulp fibers wherein the chemically treated pulp fibers have an increased or improved level of chemical retention of the water insoluble chemical additive wherein the level of chemical retention of the water insoluble chemical additive is between about 25 to about 100 percent of the applied amount of the water insoluble chemical additive when the chemically treated pulp fibers are redispersed in water. The level of chemical retention of the water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the water insoluble chemical additive. The improved level of chemical retention of the water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the water insoluble chemical additive. It is understood that the value for the lower limit is less than the value for the upper limit.
According to another embodiment of the present invention is a method for applying a water insoluble chemical additive to the pulp fiber during the pulp processing stage. During the pulp processing stage, upstream of a paper machine, one can obtain chemically treated pulp fiber. Furthermore, the chemically treated pulp fiber can be transported to several different paper machines that may be located at various sites, and the quality of the finished product from each paper machine will be more consistent. Also, by chemically treating the pulp fiber before the pulp fiber is made available for use on multiple paper machines or multiple runs on a paper machine, the need to install equipment at each paper machine for the water insoluble chemical additive addition can be eliminated.
The method of the present invention for processing pulp fibers also enables higher and more uniform concentrations of the water insoluble chemical additive to be retained by the pulp fibers while at the same time maintaining significantly lower levels of unretained water insoluble chemical additive in the water phase of a papermaking machine compared to paper machine wet end chemical additive additions.
The term xe2x80x9cunretainedxe2x80x9d refers to any portion of the chemical additive that is not retained by the pulp fiber and thus remains suspended in the process water. The term xe2x80x9cweb-forming apparatusxe2x80x9d includes fourdrinier former, twin wire former, cylinder machine, press former, crescent former, and the like of a pulp sheet machine known to those skilled in the art. The term xe2x80x9cwaterxe2x80x9d refers to water or a solution containing water and other treatment additives desired in the papermaking process. The term xe2x80x9cchemical additivexe2x80x9d refers to a single treatment compound or to a mixture of treatment compounds. It is also understood that a chemical additive used in the present invention may be an adsorbable chemical additive.
The consistency of the dried fibrous web is from about 65 to about 100 percent. In other embodiments, the consistency of the dried fibrous web is from about 80 to about 100 percent or from about 85 to about 95 percent. The consistency of the dewatered fibrous web is from about 20 to about 65 percent. In other embodiments, the consistency of the dewatered fibrous web is from about 40 to about 65 percent or from about 50 to about 65 percent. The consistency of the crumb form is from about 20 to about 85 percent. In other embodiments, the consistency of the crumb form is from about 30 to about 60 percent or from about 30 to about 45 percent.
The present method allows for the production of pulp fibers that are useful for making paper products. One aspect of the present invention is a uniform supply of chemically treated pulp fiber, replacing the need for costly and variable chemical treatments at one or more paper machines. Another aspect of the invention resides in a pulp fiber that has a higher water insoluble chemical additive loading than could otherwise be achieved in combination with either no or a relatively low level of unretained water insoluble chemical additive in the process water on a paper machine. This is because water insoluble chemical additive loading via wet end addition is often limited by the level of unadsorbed or unretained water insoluble chemical additive and/or contact time, as well as its associated processing difficulties such as foam, deposits, chemical interactions, felt plugging, excessive dryer adhesion or release or a variety of paper physical property control issues caused by the presence of unadsorbed or unretained water insoluble chemical additive in the process water on the paper machines. Another aspect of the invention is the ability to deliver pulp fiber treated with water insoluble chemical additives that would not otherwise be retained when added in the wet end of a papermaking operation.
According to one embodiment of the present invention, the method comprises adding at least a first chemical additive to pulp fiber. Pulp fibers are mixed with process water thereby forming a fiber slurry. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine. The fiber slurry is dewatered thereby forming a crumb pulp. A water insoluble chemical additive is applied to the crumb pulp thereby forming a chemically treated crumb pulp containing chemically treated pulp fibers. The chemically treated pulp fibers have an increased or improved level of chemical retention of the water insoluble chemical additive and have the level of chemical retention of the water insoluble chemical additive that is between about 25 to about 100 percent retention of the applied amount of the water insoluble chemical additive when the chemically treated pulp fibers are redispersed in water. The level of chemical retention of the water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the water insoluble chemical additive. The improved level of chemical retention of the water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the water insoluble chemical additive. It is understood that the value for the lower limit is less than the value for the upper limit.
Another aspect of the present invention resides in a method for applying water insoluble chemical additives to pulp fiber. The method comprises creating a fiber slurry comprising process water and pulp fibers. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and forming a wet fibrous web. The wet fibrous web is dewatered to a predetermined consistency thereby forming a dewatered fibrous web. A first water insoluble chemical additive is applied to the dewatered fibrous web thereby forming a chemically treated dewatered fibrous web of chemically treated pulp fibers. A second water insoluble chemical additive is applied to the chemically treated dewatered fibrous web thereby forming a dual chemically treated dewatered fibrous web containing dual chemically treated pulp fibers wherein the dual chemically treated pulp fibers have an improved level of chemical retention of the first water insoluble chemical additive and have a level of chemical retention of the first water insoluble chemical additive that is between about 25 to about 100 percent retention of the applied amount of the first water insoluble chemical additive when the dual chemically treated pulp fibers are redispersed in water and wherein the dual chemically treated pulp fibers have an improved level of chemical retention of the second water insoluble chemical additive and have a level of chemical retention of the second water insoluble chemical additive that is between about 25 to about 100 percent retention of the applied amount of the second water insoluble chemical additive when the dual chemically treated pulp fibers are redispersed in water. The level of chemical retention of the first and/or second water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the applied amount of the first and/or second water insoluble chemical additive. The improved level of chemical retention of the first and/or second water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the first and/or second water insoluble chemical additive, respectively. It is understood that the value for the lower limit is less than the value for the upper limit.
Another aspect of the present invention resides in a method for applying water insoluble chemical additives to pulp fiber. The method comprises mixing pulp fibers with process water to form a fiber slurry. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and forming a wet fibrous web. The wet fibrous web is dewatered to a predetermined consistency thereby forming a dewatered fibrous web. The dewatered fibrous web is dried to a predetermined consistency thereby forming a dried fibrous web. A first water insoluble chemical additive is applied to the dried fibrous web and applying a second water insoluble chemical additive to the dried fibrous web, thereby forming a dual chemically treated dewatered fibrous web containing dual chemically treated pulp fibers wherein the dual chemically treated pulp fibers have an improved level of chemical retention of the first water insoluble chemical additive and have a level of chemical retention of the first water insoluble chemical additive is between about 25 to about 100 percent retention of the applied amount of the first water insoluble chemical additive when the dual chemically treated pulp fibers are redispersed in water and wherein the dual chemically treated pulp fibers have an improved level of chemical retention of the second water insoluble chemical additive and have a level of chemical retention of the second water insoluble chemical additive is between about 25 to about 100 percent retention of the applied second water insoluble chemical additive when the dual chemically treated pulp fibers are redispersed in water. The level of chemical retention of the first and/or second water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the applied amount of the first and/or second water insoluble chemical additive. The improved level of chemical retention of the first and/or second water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the first and/or second water insoluble chemical additive, respectively. It is understood that the value for the lower limit is less than the value for the upper limit. A finished product having enhanced qualities due to the retention of the chemical additive by the pulp fibers may be produced.
Another aspect of the present invention resides in a method for applying water insoluble chemical additives to pulp fiber. The method comprises mixing pulp fibers with process water to form a fiber slurry. The fiber slurry is transported to a web-forming apparatus of a pulp sheet machine and forming a wet fibrous web. The wet fibrous web is dewatered to a predetermined consistency thereby forming a dewatered fibrous web. Applying a first water insoluble chemical additive to the dewatered fibrous web to the dewatered fibrous web thereby forming a chemically treated dewatered fibrous web. The chemically treated dewatered fibrous web is dried to a predetermined consistency thereby forming a chemically treated dried fibrous web. A second water insoluble chemical additive is applied to the chemically treated dried fibrous web, thereby forming a dual chemically treated dried fibrous web containing dual chemically treated pulp fibers wherein the dual chemically treated pulp fibers have an improved level of chemical retention of the first water insoluble chemical additive and have a level of chemical retention of the first water insoluble chemical additive that is between about 25 to about 100 percent retention of the applied amount of the first water insoluble chemical additive when the dual chemically treated pulp fibers are redispersed in water and wherein the dual chemically treated pulp fibers have an improved level of chemical retention of the second water insoluble chemical additive and have a level of chemical retention of the second water insoluble chemical additive that is between about 25 to about 100 percent retention of the applied amount of the second water insoluble chemical additive when the dual chemically treated pulp fibers are redispersed in water. The level of chemical retention of the first and/or second water insoluble chemical additive may range from between about 60 to about 100 percent or between about 80 to about 100 percent retention of the applied amount of the first and/or second water insoluble chemical additive. The improved level of chemical retention of the first and/or second water insoluble chemical additive, measured as the change in the level of chemical retention of adding by typical wet-end addition, may range from a lower limit of about 5 percent, about 15 percent, about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, and about 75 percent to a higher limit of about 25 percent, about 35 percent, about 45 percent, about 55 percent, about 65 percent, about 75 percent, about 85 percent, about 95 percent, and about 100 percent retention of the first and/or second water insoluble chemical additive, respectively. It is understood that the value for the lower limit is less than the value for the upper limit. A finished product having enhanced qualities due to the retention of the chemical additive by the pulp fibers may be produced.
The present invention is particularly useful for adding water insoluble chemical additives such as softening agents to the pulp fibers, allowing for the less problematic and lower cost production of finished products having enhanced qualities provided by the retained water insoluble chemical additives by the pulp fibers.
Hence, another aspect of the present invention resides in paper products formed from pulp fibers that have been chemically treated to minimize the amount of residual, unretained water insoluble chemical additives in the process water on a paper machine. The term xe2x80x9cpaperxe2x80x9d is used herein to broadly include writing, printing, wrapping, sanitary, and industrial papers, newsprint, linerboard, tissue, bath tissue, facial tissue, napkins, wipers, and towels, along with other cellulose structures including absorbent pads, intake webs in absorbent articles such as diapers, bed pads, wet wipes, meat and poultry pads, feminine care pads, and the like made in accordance with any conventional process for the production of such products. With regard to the use of the term xe2x80x9cpaperxe2x80x9d as used herein includes any fibrous web containing cellulosic fibers alone or in combination with other fibers, natural or synthetic. It can be layered or unlayered, creped or uncreped, and can consist of a single ply or multiple plies. In addition, the paper or tissue web can contain reinforcing fibers for integrity and strength.
The term xe2x80x9csoftening agentxe2x80x9d refers to any water insoluble chemical additive that can be incorporated into paper products such as tissue to provide improved runnability, tactile feel, and reduce paper stiffness. These water insoluble chemical additives can also act to reduce paper stiffness or can act solely to improve the surface characteristics of tissue, such as by reducing the coefficient of friction between the tissue surface and the hand.
The term xe2x80x9cdyexe2x80x9d refers to any chemical that can be incorporated into paper products, such as bathroom tissue, facial tissue, paper towels, and napkins, to impart a color. Depending on the nature of the chemical, dyes may be classified as acid dyes, basic dyes, direct dyes, cellulose reactive dyes, or pigments. All classifications are suitable for use in conjunction with the present invention.
The term xe2x80x9cwater insolublexe2x80x9d refers to solids or liquids that will not form a solution in water, and the term xe2x80x9cwater dispersiblexe2x80x9d refers to solids or liquids of colloidal size or larger that can be dispersed into an aqueous medium.
The term xe2x80x9cbonding agentxe2x80x9d refers to any chemical that can be incorporated into tissue to increase or enhance the level of interfiber or intrafiber bonding in the sheet. The increased bonding can be either ionic, Hydrogen or covalent in nature. It is understood that a bonding agent refers to both dry and wet strength enhancing chemical additives.
The method for applying water insoluble chemical additives to the pulp fibers may be used in a wide variety of pulp finishing processing, including dry lap pulp, wet lap pulp, crumb pulp, and flash dried pulp operations. By way of illustration, various pulp finishing processes (also referred to as pulp processing) are disclosed in Pulp and Paper Manufacture: The Pulping of Wood, 2nd Ed., Volume 1, Chapter 12. Ronald G. MacDonald, editor, which is incorporated by reference. Various methods may be used to apply the water insoluble chemical additives in the present invention, including, but not limited to: spraying, coating, foaming, printing, size pressing, or any other method known in the art.
In addition, in situations where more than one water insoluble chemical additive is to be employed, the water insoluble chemical additives may be added to the fibrous web in sequence to reduce interactions between the water insoluble chemical additives.
Many pulp fiber types may be used for the present invention including hardwood or softwoods, straw, flax, milkweed seed floss fibers, abaca, hemp, kenaf, bagasse, cotton, reed, and the like. All known papermaking fibers may be used, including bleached and unbleached fibers, fibers of natural origin (including wood fiber and other cellulose fibers, cellulose derivatives, and chemically stiffened or crosslinked fibers), some component portion of synthetic fiber (synthetic papermaking fibers include certain forms of fibers made from polypropylene, acrylic, aramids, acetates, and the like), virgin and recovered or recycled fibers, hardwood and softwood, and fibers that have been mechanically pulped (e.g., groundwood), chemically pulped (including but not limited to the kraft and sulfite pulp processings), thermomechanically pulped, chemithermomechanically pulped, and the like. Mixtures of any subset of the above mentioned or related fiber classes may be used. The pulp fibers can be prepared in a multiplicity of ways known to be advantageous in the art. Useful methods of preparing fibers include dispersion to impart curl and improved drying properties, such as disclosed in U.S. Pat. Nos. 5,348,620 issued Sep. 20, 1994 and 5,501,768 issued Mar. 26, 1996, both to M. A. Hermans et al. and 5,656,132 issued Aug. 12, 1997 to Farrington, Jr. et al.
According to the present invention, the chemical treatment of the pulp fibers may occur prior to, during, or after the drying phase of the pulp processing. The generally accepted methods of drying include flash drying, can drying, flack drying, through air drying, Infra-red drying, fluidized bed, or any method of drying known in the art. The present invention may also be applied to wet lap pulp processes without the use of dryers.
Numerous features and advantages of the present invention will appear from the following description. In the description, reference is made to the accompanying drawings which illustrate preferred embodiments of the invention. Such embodiments do not represent the full scope of the invention. Reference should therefore be made to the claims herein for interpreting the full scope of the invention.